The claim here is that veganism has some potential negative health effect on the human body. It could be big; it could be small. E.g.
Or let's try this one out: nearly every major pandemic disease is the result of animal agriculture or consuming animal products - setting aside even COVID - there's SARS, MERS, swine flu, bird flu, Spanish flu, among others that have not made the pass to humans. Let alone the fact that farm animals have the vast majority of antibiotic abuse that could easily lead to more antibiotic resistant flesh-eating bacteria that can only be treated by amputation. Do you think it might be worth not consuming animal products because there could be another global pandemic? Consider that a majority of slaughtered pigs have lung lesions consistent with pneumonia. Somehow, I think we ought to treat this idea seriously, because, if recent events are any indication, this isn't exactly a grenade you want to hang on the wall by the pin.
For all the speculation that carnists offer on potentially low this or that, heart disease, stroke, diabetes, and kidney disease (often related to high blood pressure) are on the top 10 list year in and year out, in addition to cancers attributable directly to eating of red meat. So for every concern troll pretending to care about health online, a real person dies.
You can't participate in the definite torture and killing of an animal, hurting other people and yourself in the process, because you want to cherry-pick, out of the minor health effects that might happen down the road, a few (usually extremely avoidable) ones that apply to veganism. That just isn't a real argument.